Hello and welcome,
The physical symptoms you describe may well be related to your mental health. Acid reflux is commonly associated with anxiety and panic however the nature of the relationship between the two is still being explored. There is research evidence both that anxiety predisposes people to developing the condition and that some psychiatric medication may worsen the symptoms. Here is an article which mentions anxiety and depression as pre-disposing factors: http://panicdisorder.about.com/od/relatedconditions/a/GERD.htm
Similarly headaches, dizziness and nausea are all symptoms of anxiety. As immunity is related to general well being, t may be that a combination of the physical symptoms and mental stress is lowering your immunity to colds and viruses. If left untreated, anxiety may worsen and lead to other problems such as feeling low and this may lead to depression.
For all of these reasons, I would recommend you consulting your doctor and asking for a recommendation for psychotherapy. An effective treatment for anxiety related problems is cognitive behavioural therapy.
I hope this answer is helpful, please do reply if you have any questions of comments.
All the best,
It's important that you see the doctor if you don't feel the medication is working, my understanding is that the condition can be managed effectively over a long time without serious complications. Such complications usually only develop if the condition is not treated and so worsens. I am not a medical expect so you may wish to post a question about this in the medical forum.
If anxiety is a trigger, as it often is, then treating the panic disorder may help a lot. It would also improve your quality of life as you are currently worried and anxious much of the time. The National Institute for Clinical Excellence (who make recommendations to doctors on what type of treatments to offer, based on clinical trials of medicines and treatments) recommend Cognitive Behavioural Therapy (CBT) for panic disorder. this is why I feel you may benefit from this treatment.
Hypnotherapy may help a little, especially with relaxation, however I would not recommend it as it does not get to the root cause and so often the effect wears off over time. The root causes of the panic disorder are both the negative thinking that you mention and the body sensations you experience when you get the panic. CBT has specific interventions designed to alter these. I see you are in the UK. Within the last few years CBT has become more widely available via GPs. There is usually a waiting list but it may be that you can access it free of charge via the NHS.
I'll attach a link to a leaflet on panic disorder, I hope you find it helpful. http://www.ntw.nhs.uk/pic/leaflets/Panic%20A4%202010.pdf
Please do let me know if I can be of any further help.